1. Field of the Invention
The present invention relates to an active handoff system and method of a dual mode mobile terminal capable of connecting to different kinds of networks. More particularly, the present invention relates to an active handoff system and method of a dual mode mobile terminal enabling a handoff of a dual mode mobile terminal having an Internet Protocol (IP) address assigned by a mobile communication system, between the mobile communication system and a wireless network, for example a wireless local area network (LAN), without change in the IP address of the mobile terminal.
2. Description of the Related Art
In General, “handoff” refers to a function that prevents call disconnection in a process of moving from one base station to another as a mobile phone user moves.
Mobile phone handoffs include a soft handoff performed between base stations, a hard handoff performed between converters, and a softer handoff performed between sectors of a base station.
The soft handoff is a technique by which a base station disconnects a signal of a mobile phone user after the signal is received by another base station, and the hard handoff is a technique by which a base station transfers a signal of a mobile phone user after disconnecting the signal.
Accordingly, a conventional handoff is performed within a single network.
In relation to a method of performing a conventional handoff between different kinds of networks, FIG. 1 illustrates the case of moving from a wireless LAN region 2 to a cellular network region 1 using a mobile IP address of a dual mode mobile terminal.
As mentioned above, a conventional handoff between different kinds of networks is performed by a mobile communication system equipped with Packet Data Serving Node (PDSN) 11 and base stations (BSS) 12, and a wireless LAN equipped with an Access Router (AR) 21 and an Access Point (AP) 22, 4, a Correspondent Node (CN) 3 host equipped with a Home Agent (HA) 31, and a dual mode mobile terminal.
The PDSN of the mobile communication system is an exchange network providing a mobile terminal connecting to an IP network through a mobile communication system and the terminal's user with a charging/authentication function, a Point-to-Point (PPP) connection function, an IP routing function, a vertical handoff function, and so on.
Also, if mobile IP is supported, an external identification agent is employed.
The base station of the mobile communication system is composed of equipment for managing a wireless connection standard of a mobile terminal connecting to the mobile communication system.
The AR of the wireless LAN provides a mobile terminal connecting to an IP network through a mobile communication system and the terminal's user with a charging/authentication function, a PPP connection function, an IP routing function, a vertical handoff function, etc.
Also, if mobile IP is supported, an external identification agent is employed.
The AP of the wireless LAN manages connection standards between the mobile terminal connecting to the wireless LAN and the wireless LAN, and serves as a bridge between the wireless LAN and a wired LAN.
The HA is equipment that supports a mobile IP function.
Also, the CN refers to a server and host that can be connected to through the dual mode mobile terminal and the IP network and perform data communication or provide service to a user.
Lastly, the dual mode mobile terminal is a terminal that can connect to both a wireless LAN and a mobile communication system.
In such a convention method of handoff between different kinds of networks, a mobile terminal using a home IP address can continue to use the same address even after moving from a wireless LAN to a 3G mobile communication network, and the home agent takes over and forwards all packets transmitted to the terminal to a network in which the terminal is actually located. Thus, the method enables a handoff that is, to a predetermined extent, not subject to disconnection.
However, in the conventional method of handoff between different kinds of networks, a delay can occur due to signal transmission and mobility estimation which varies with mobile IP, resulting in a problem of traffic congestion at the home agent, and so on. Consequently, mobile IP addresses are not supported in 3G mobile communication systems currently in use.